Tabletop gaming spawned from a hobby introduced to civilians late in Queen Victoria’s reign: wargaming. Centuries prior, the predecessor to Dungeons and Dragons (or even more directly to Warhammer) was a pursuit of field officers. That military pedigree persists sub rosa in most modern tabletop role-playing games. Even games light in combat (Pandemonium, for example) still feature conflict resolution mechanics developed to overcome otherwise-intractable disputes that naturally arise in play.
It is therefore curious to me then that military affairs are so often given short shrift in so many of these game systems. Army divisions, such as they are, tend to be cut and pasted from Hollywood versions of medieval organization, with some themed battalions thrown in for color. Mostly it’s infantry, archery, and a bit of cavalry. If you’re lucky, you’ve got some war mages, maybe air cav (hippogriffs, wyverns, et al), and a couple of exotic units. Dwarves might sign up as sappers, or gnomes as part of a skunkworks R&D team, but apart from flavor text, you still roll pretty much the same attack and damage dice, and they act as mere reskinned versions of standard units.
This is a grave oversight. Wartime organization has always been optimized to counter existing (or anticipated) threats using the most economical* technology. While I can’t speak for the regular armies of yore, I can assure you that much of Soldiers’ and Sailors’ peacetime activity is spent drilling. On my boat, we alternated workups between the Tactical Readiness Examination and the Operational Reactor Safeguard Examination. TRE was held on even-numbered patrols; ORSE was on odd-numbered patrols. The actual examinations were held after our alert period had ended, which meant that most of the underway period was spent practicing for a missile launch, sub-to-surface combat, sub-to-sub combat, or some sort of shipboard casualty. We Nukes had it the worst, since we had duties for both TRE and ORSE while the forward area guys only had to participate in the TRE (more or less**).
And that’s just for line combatants. If you want to get all nice and recursive, wargaming should be an in-game hobby for military NPC. Sharpening tactical thinking is at least as important as honing steel. Prior to that, the development of arms, armor, and battlefield organization follows an evolutionarily-stable strategy against actual or likely opponents. The victorious prince will allow his generals the luxury of building armies capable of defeating the enemy. For the manpower-rich French, this means equipping serfs with cheap, easy-to-fire crossbows. For the English, this means hiring highly-trained Welsh longbowmen. You go to war with the army you have, so you’d better make sure it’s suited to the battles you’re likely to fight.
So what battles are you likely to fight? Orc assaults will likely rely on superior infantry numbers, Gnoll infestations will be guerilla-style salt-the-earth raids, Illithid conflicts will be psy-op 4GW affairs, and if you have a dragon problem, you can kiss those thatched roof cottages goodbye (pace Trogdor). Will your bog-standard infantry/archery/cavalry mix be suited to defend the kingdom against these sorts of threats? How about your org chart? Do you use a regimental structure? Brigade? Semi-autonomous cells? What about your navies? What constitutes a standard fleet? Do you have a marine force? Littoral combat? What influence do exotic maritime threats have on hull size and cladding? What sort of subsurface countermeasures have your research teams developed?
Moreover, I have to confess that a trope that has long irked me is that of the Isolationist Undersea Kingdom. Do you mean to seriously propose that King Triton, a long-lived monarch, would forgo hundreds, if not thousands of years of mutually-beneficial exchange to what end, exactly? Pride? The degree of specialization inherent in such wildly different environments necessarily implies immense degrees of comparative advantage. The sheer quantity of wealth left on the table from maintaining strict land/sea separation is mind-boggling. It far surpasses Tokugawa-era levels of chauvinism, veering into DPRK territory. Even something as simple as an anti-pollution treaty seems beyond the imagination of your typical writer of undersea tales. “You stop dumping your trash into my kingdom, and I’ll make sure your dead sailors get a proper burial instead of ending up as waterlogged zombies that periodically wash ashore to terrorize your fishing villages,” hardly seems too far a bridge.
The same logic applies to most other isolated societies, but the trope seems reserved most strongly for underwater kingdoms. Maybe mix it up a little next time and have your stand-in for totalitarian regimes be set in the desert or a swamp or something. No need to beleaguer the poor tritons and merfolk of your world.
Next time, let’s consider the relationship between military technology and settlement design. Have you ever been to the older parts of European cities? Have you seen the old walls? The keep? Would that be a sensible design to defend against umber hulks? How about graveyard placement in a world with powerful necromancers?
*By “economical” I mean the most advanced materiel available in sufficient quantities within the budget constraint. It doesn’t mean “cheap”.
**If you’re a former torpedoman, I trust you’ll allow me a bit of poetic license here. Yes, I know you had to get your DC gear ready and hang out in the Crew’s Mess during the occasional fire drill, but you didn’t have to bolt back to the engineroom in your grundy undies halfway through your off-watch when the PPCA blared.